Gnome complains bitterly when it starts that the CleanBig theme is missing.
If CleanBig should have been present, there should have been a rpm
dependency that made the upgrade procedure pull it in, or gnome should be
set up such that it silently falls back to default (no theme) appearance.

the upgrade cannot possibly remove dependencies from your home dir. It knows
nothing about it. What if you have 1000 users mounted over NFS? What if you
have your home in /foo/bar. RPMS do _not_ touch users data. (-:

Point taken. But how did it (CleanBig) get in there in the first place?
I did not explicitely do that. It may not be practical to fix, but it is not
welcome to be confronted with a complaint that something went
missing that I didn't even know was there in the first place!
And why was CleanBig removed if it was referenced? I didn't ask
for that either!